Metals such as aluminum alloys have been widely used for years as structural components in various applications such as aircraft, motor vehicles, and countless other applications. More recently, composite materials such as carbon fiber reinforced polymer (CFRP) have been used. These composite materials can provide advantages in strength to weight ratio, and they have been increasingly deployed as replacement materials for metal in structural components. However, composite materials cannot be used as a universal replacement for metal, as they suffer from other limitations associated with electrical conductivity or poor heat resistance, which necessitate the continued use of metal components in applications where electrical conductivity, heat resistance, abrasion resistance, or other properties commonly associated with metals are required. Accordingly, in many applications, both metal materials and composite materials are used in proximity to one another and must often be connected together.
The connection of composite materials to metal presents a number of technical challenges. Conventional techniques, such as attaching a metal sheath or a metal article to a composite surface with adhesive, are subject to a variety of bond failure modes, including adhesive failure at either the metal-adhesive interface or at the composite-adhesive interface and/or cohesive failure of the adhesive itself. These failure modes can be promoted by exposure of the adhesive bond to extreme conditions such as temperature, radiation, or moisture. Direct application of metal coatings through spray techniques such as cold spray can cause significant erosion of the relatively brittle thermoset resins used in the composite materials to the point where the loss of material from such erosion overwhelms any adhesion of any metal to the composite substrate.
In view of the above, there remains a need to develop alternative materials and techniques for bonding or connecting composite materials and metals.